Doraemon: Nobita no Ningyo Daikaisen

Nobita requests a place to dive, prompting Doraemon to create an artificial ocean using gadgets, allowing them to swim at a higher elevation. After turning off the illusion, a mermaid named Sophia appears in Nobita’s backyard. She is a princess from an ancient underwater civilization. Doraemon, Nobita, Shizuka, Gian, and Suneo befriend her and are invited to her underwater kingdom. On their way, they encounter a conflict between mermaids and a rival tribe that had expelled them from their planet long ago. Nobita, Doraemon, and their friends help Sophia search for a legendary sword that could restore peace to the ocean.